Courtney Carter, Age 12, Of Indianapolis, Ind., for his question:
Why is the surface of Venus so hot?
Venus is veiled in a dense and cloudy atmosphere. Reliable information about conditions on the surface of our sister planet has been very scarce until now. On dec. 14, 1962, the space prober Mariner II came close enough to scan the face of Venus and sent back to earth millions of facts recorded by its scientific instruments.
The mass of data received frown mariner ii is still being evaluated. The little space prober came within 21,700 miles of Venus, which is closer than the moon every comes to the earth. It rushed past when half the golden planet was in daylight and half in darkness, and its nodding instruments scanned up the dark side, down the twilight zone and up the sunlit side.
According to reports from mariner ii, the ground temperature all over the planet Venus is 800 fahrenheit degrees. A space ship designed to land on Venus must have no parts of tin, zinc or lead, for these metals would melt in the searing heat.
Mariner II found no magnetic fields around Venus. This and other items suggest that the planet revolves maybe once while it orbits the sun. One side of the globe, then, may be constantly turned toward the sun, as the same side of the moon forever faces the earth. The opposite side of Venus is most likely shrouded in eternal night. The dark side of mercury is as cold as outer space, and each night the earth loses some of its daytime heat. But mariner II reports that daylight, twilight and night on Venus have the same temperature.
Scientists explain this fact, along with the high temperature of Venus, by what they call the greenhouse effect. The atmosphere of Venus is 10 to 20 times denser than our atmosphere, and its thick clouds begin about 45 miles above the ground. The sun's energy pierces through the clouds in the form of light. It is absorbed by the rough, sandy ground, and the infrared rays of the solar energy become heat. The heat is radiated back into the air, but the smoggy clouds of carbon dioxide and hydrocarbons absorb infrared heat and blanket its escape. Solar heatwis gathered and accumulated on the sunlit side of Venus. In the cloud free level above the ground, slow winds distribute the heat evenly betweeri the day arid night sides of the planet.
This greenhouse effect occurs on a much smaller scale over our own smoggy cities. On a hot day, solar energy pierces the hazy ceiling as light. When it reaches the solid ground, some of this energy becomes heat. After sunset, the day's heat rises, but it cannot escape high into the cool atmosphere, which is normal in other areas. Much of the heat is absorbed and held in the smoggy air. A smog city does not cool off at night as much as it would if the air above it were smog free.
Venus Statistics
Planetary Symbol: Name in Roman/Greek Mythology: Venus/Aphrodite
Diameter: 12,104 km (7,522 miles)
Rotation Period about Axis: 243 days (retrograde)
Mass: 4.87x10^24 kilograms (0.82 x Earth's)
Revolution Period about the Sun: 0.62 years
Density: 5,243 kg/m^3 Tilt of Axis: 177-178o
Minimum Distance from Sun: 108 million km (67 million miles)
Surface Gravity: 8.87 m/s^2 (0.90 x Earth's)
Maximum Distance from Sun: 109 million km (68 million miles)
Average Temperature (C/F): 457o C (855o F)
Average Surface Temperature (K): 730K
Orbital Semi-major Axis: 0.72 AU (Earth=1 AU)
Minimum Distance from Earth: 40 million km (25 million miles)
Satellites: 0